WO2023127760A1 - Power conversion device - Google Patents

Abstract

A power conversion device according to one aspect of the present invention comprises a power conversion circuit that converts DC power and N-phase AC power (N represents an integer greater than or equal to 3) to each other, and a control unit that controls 2N switches included in the power conversion circuit in a first modulation mode. The control unit in the first modulation mode periodically switches between a first PWM mode in which, among the 2N switches, a high-side switch or low-side switch corresponding to one phase is fixed in an ON position and the switches corresponding to the other phases are controlled by pulse width modulation, and a second PWM mode in which, among the 2N switches, the switches corresponding to all the phases are controlled by pulse width modulation. The sum of a first period in which the control unit operates in the first PWM mode and a second period in which the control unit operates in the second PWM mode is shorter than one-2Nth of one cycle of the electrical angle of an AC waveform occurring at a connection terminal of the power conversion circuit. The first period is longer than or equal to one cycle of pulse width modulation. The proportion of the first period in the sum of the first period and the second period is variable.

Description

power converter

The present invention relates to a power converter.

Conventionally, two-phase modulation in which a high-side switch or a low-side switch of one phase out of six switches included in a power conversion circuit such as a three-phase inverter is fixed on, and the switches of the remaining phases are controlled by pulse width modulation. and a three-phase modulation system in which all phase switches out of six switches are controlled by pulse width modulation.

The two-phase modulation method has the advantage of low switching loss, but has the disadvantage of large noise due to large phase current ripple. The three-phase modulation method has the advantage that the phase current ripple is small (the noise is small) and highly accurate motor control with little torque unevenness can be realized, but it has the disadvantage that the switching loss is large.

There is a conventional technical idea of controlling a power conversion circuit while switching between a two-phase modulation method and a three-phase modulation method. There is a risk that the torque of the motor will fluctuate due to the sudden change, and that the user will feel uncomfortable due to the sudden change in noise.

In Patent Document 1, the three-phase modulation method is used when the modulation rate is small, and the modulation method is continuously changed from the three-phase modulation method to the two-phase modulation method as the modulation rate increases. Techniques for suppressing sudden changes in noise caused by switching to the two-phase modulation method have been disclosed.

WO2010/119929

In the technique of Patent Document 1, the sum of a pair of three-phase modulation period and two-phase modulation period adjacent on the time axis is reduced to 1/6 of one cycle of the electrical angle of the AC waveform appearing at the connection terminal of the power conversion circuit. In a fixed state, the three-phase modulation method and the two-phase modulation method are alternately switched. In this case, torque unevenness may occur due to changes in switching loss at the timing of switching between the three-phase modulation method and the two-phase modulation method.

One aspect of the power conversion apparatus of the present invention includes a power conversion circuit that performs mutual conversion between DC power and N-phase AC power (N is an integer of 3 or more), and 2N switches included in the power conversion circuit. a control unit that controls in a first modulation mode, wherein the control unit fixes one phase high-side switch or low-side switch of the 2N switches to ON in the first modulation mode, periodically switching between a first PWM mode in which the remaining phase switches are controlled by pulse width modulation and a second PWM mode in which all phase switches among the 2N switches are controlled by the pulse width modulation; The sum of the first period during which the control section operates in the first PWM mode and the second period during which the control section operates in the second PWM mode appears at the connection terminal of the power conversion circuit. The first period is shorter than 1/2N of one cycle of the electrical angle of the AC waveform, the first period is longer than one cycle of the pulse width modulation, and the length of the first period and the second period is The ratio of the first period to the sum is variable.

According to the above aspect of the present invention, a power converter capable of suppressing torque unevenness is provided.

FIG. 1 is a circuit block diagram schematically showing the configuration of a power converter according to a first embodiment of the present invention. FIG. 2 is a diagram showing an example of each high-side gate signal output during a period when the control section in the first embodiment operates in the first modulation mode. FIG. 3 is a diagram showing phase current waveforms obtained by performing a simulation assuming that each switch is controlled in the first modulation mode using the gate signals shown in FIG. FIG. 4 is a diagram showing the magnitude of the phase current ripple shown in FIG. 3 as a standard deviation of current values. FIG. 5 is a diagram showing an example of each high-side gate signal output during periods when the control unit in the second embodiment operates in each of the first modulation mode, the second modulation mode, and the third modulation mode. be. FIG. 6 is a diagram showing an example of each high-side gate signal output while the control unit in the third embodiment operates in each of the first modulation mode, the second modulation mode, and the third modulation mode. be. FIG. 7 is a diagram showing an example of each high-side gate signal output during periods when the control unit in the fourth embodiment operates in each of the first modulation mode, the second modulation mode, and the third modulation mode. be. FIG. 8 is a diagram showing an example of each high-side gate signal output during periods when the control unit in the fifth embodiment operates in each of the first modulation mode, the second modulation mode, and the third modulation mode. be. FIG. 9 is a diagram showing a specific example of mode ratios in the third embodiment. FIG. 10 is a diagram showing a specific example of mode ratios in the fifth embodiment.

An embodiment of the present invention will be described in detail below with reference to the drawings. [First Embodiment]
First, a first embodiment of the present invention will be described. FIG. 1 is a circuit block diagram schematically showing the configuration of a power converter 10 according to the first embodiment. As shown in FIG. 1 , the power conversion device 10 is connected with a motor 20 . As an example, the motor 20 is an inner rotor type three-phase brushless DC motor. Also, the motor 20 is, for example, a drive motor (traction motor) mounted on an electric vehicle.

The motor 20 has a U-phase terminal 21u, a V-phase terminal 21v, a W-phase terminal 21w, a U-phase coil 22u, a V-phase coil 22v, and a W-phase coil 22w. Although not shown in FIG. 1, the motor 20 has a motor case, and a rotor and a stator housed in the motor case. The rotor is a rotating body that is rotatably supported inside the motor case by a bearing component such as a rotor bearing. The rotor has an output shaft coaxially joined with the rotor while axially passing through the radially inner side of the rotor. The stator is fixed inside the motor case so as to surround the outer peripheral surface of the rotor, and generates an electromagnetic force necessary to rotate the rotor.

The U-phase terminal 21u, the V-phase terminal 21v, and the W-phase terminal 21w are metal terminals exposed from the surface of the motor case. U-phase terminal 21 u is connected to U-phase connection terminal 13 u of power converter 10 . V-phase terminal 21v is connected to V-phase connection terminal 13v of power converter 10 . The W-phase terminal 21w is connected to the W-phase connection terminal 13w of the power converter 10 . The U-phase coil 22u, the V-phase coil 22v, and the W-phase coil 22w are excitation coils provided in the stator, respectively. As an example, the U-phase coil 22u, the V-phase coil 22v, and the W-phase coil 22w are star-connected inside the motor 20 .

The U-phase coil 22u is connected between the U-phase terminal 21u and the neutral point N. V-phase coil 22v is connected between V-phase terminal 21v and neutral point N. The W-phase coil 22w is connected between the W-phase terminal 21w and the neutral point N. By controlling the energized states of the U-phase coil 22u, the V-phase coil 22v, and the W-phase coil 22w by the power converter 10, an electromagnetic force necessary to rotate the rotor is generated. As the rotor rotates, the output shaft also rotates in synchronization with the rotor.

The power conversion device 10 includes a power conversion circuit 11 and a control section 12 . The power conversion circuit 11 is connected to the motor 20 and the DC power supply 30, and performs mutual conversion between DC power and N-phase AC power (N is an integer of 3 or more). In this embodiment, the value of N is 3 because the motor 20 is a three-phase motor. Therefore, the power conversion circuit 11 performs mutual conversion between DC power and three-phase AC power. For example, when the power conversion circuit 11 functions as an inverter, the power conversion circuit 11 converts DC power supplied from the DC power supply 30 into three-phase AC power and outputs the three-phase AC power to the motor 20 . As an example, DC power supply 30 is one of a plurality of batteries mounted on an electric vehicle.

The power conversion circuit 11 includes 2N switches. As described above, in this embodiment, the value of N is 3, so the power conversion circuit 11 includes 6 switches. The power conversion circuit 11 includes a U-phase high-side switch _QUH , a V-phase high-side switch _QVH , a W-phase high-side switch _QWH , a U-phase low-side switch _QUL , a V-phase low-side switch _QVL , and a W-phase switch QWL. and a phase low side switch _QWL . Each switch in this embodiment is, for example, an IGBT (Insulated Gate Bipolar Transistor).

A collector terminal of the U-phase high-side switch _QUH , a collector terminal of the V-phase high-side switch _QVH , and a collector terminal of the W-phase high-side switch _QWH are connected to the positive terminal of the DC power supply 30, respectively. The emitter terminal of the U-phase low-side switch _QUL , the emitter terminal of the V-phase low-side switch _QVL , and the emitter terminal of the W-phase low-side switch _QWL are connected to the negative terminal of the DC power supply 30, respectively.

The emitter terminal of the U-phase high side switch _QUH is connected to the U-phase connection terminal 13u and the collector terminal of the U-phase low side switch _QUL , respectively. That is, the emitter terminal of the U-phase high side switch _QUH is connected to the U-phase terminal 21u of the motor 20 via the U-phase connection terminal 13u. The emitter terminal of the V-phase high side switch _QVH is connected to the V-phase connection terminal 13v and the collector terminal of the V-phase low side switch _QVL , respectively. That is, the emitter terminal of the V-phase high-side switch _QVH is connected to the V-phase terminal 21v of the motor 20 via the V-phase connection terminal 13v. The emitter terminal of the W-phase high side switch _QWH is connected to the W-phase connection terminal 13w and the collector terminal of the W-phase low side switch _QWL . That is, the emitter terminal of the W-phase high side switch _QWH is connected to the W-phase terminal 21w of the motor 20 via the W-phase connection terminal 13w.

A gate terminal of the U-phase high-side switch _QUH , a gate terminal of the V-phase high-side switch _QVH , and a gate terminal of the W-phase high-side switch _QWH are connected to the control section 12, respectively. The gate terminal of the U-phase low-side switch _QUL , the gate terminal of the V-phase low-side switch _QVL , and the gate terminal of the W-phase low-side switch _QWL are also connected to the controller 12, respectively.

As described above, the power conversion circuit 11 is configured by a three-phase full-bridge circuit having three high-side switches and three low-side switches. The power conversion circuit 11 configured in this manner performs mutual conversion between DC power and three-phase AC power by controlling switching of each switch by the control unit 12 . A U-phase connection terminal 13u, a V-phase connection terminal 13v, and a W-phase connection terminal 13w are connection terminals of the power conversion circuit 11 .

The control unit 12 is a processor containing a memory (not shown). As an example, the control unit 12 is an MCU (Microcontroller Unit). The control unit 12 controls the power conversion circuit 11 according to a program pre-stored in the memory. Although the details will be described later, the control unit 12 controls the six switches included in the power conversion circuit 11 in the first modulation mode. The controller 12 generates gate signals necessary to control the six switches in the first modulation mode.

The control unit 12 generates a U-phase high-side gate signal G1 necessary for controlling the U-phase high-side switch _QUH , and transmits the generated U-phase high-side gate signal G1 to the gate terminal of the U-phase high-side switch _QUH. output to The control unit 12 generates a U-phase low-side gate signal G2 necessary for controlling the U-phase low-side switch _QUL , and outputs the generated U-phase low-side gate signal G2 to the gate terminal of the U-phase low-side switch _QUL . The U-phase low-side gate signal G2 is a complementary signal of the U-phase high-side gate signal G1.

The control unit 12 generates a V-phase high-side gate signal G3 necessary for controlling the V-phase high-side switch _QVH , and transmits the generated V-phase high-side gate signal G3 to the gate terminal of the V-phase high-side switch _QVH. output to The control unit 12 generates a V-phase low-side gate signal G4 necessary for controlling the V-phase low-side switch _QVL , and outputs the generated V-phase low-side gate signal G4 to the gate terminal of the V-phase low-side switch _QVL . The V-phase low side gate signal G4 is a complementary signal of the V-phase high side gate signal G3.

The control unit 12 generates a W-phase high-side gate signal G5 necessary for controlling the W-phase high-side switch _QWH , and transmits the generated W-phase high-side gate signal G5 to the gate terminal of the W-phase high-side switch _QWH. output to The control unit 12 generates a W-phase low-side gate signal G6 necessary for controlling the W-phase low-side switch _QWL , and outputs the generated W-phase low-side gate signal G6 to the gate terminal of the W-phase low-side switch _QWL . The W-phase low-side gate signal G6 is a complementary signal of the W-phase high-side gate signal G5.

A dead time is inserted into each gate signal to prevent the high-side switch and low-side switch of the same phase from being switched on at the same time.

Below, the operation of the control unit 12 included in the power converter 10 configured as described above will be described in detail. The control unit 12 has a first modulation mode as a modulation mode. The control unit 12 controls the six switches included in the power conversion circuit 11 in the first modulation mode.

FIG. 2 shows an example of the U-phase high-side gate signal G1, the V-phase high-side gate signal G3, and the W-phase high-side gate signal G5 that are output during the period TM1 in which the control section 12 operates in the first modulation mode. It is a diagram. Since each low side gate signal is a complementary signal of each high side gate signal, illustration of each low side gate signal is omitted in FIG. In the following description, the period TM1 during which the control section 12 operates in the first modulation mode may be referred to as the first modulation mode period.

In the first modulation mode, the control unit 12 fixes the high-side switch or low-side switch of one phase among the six switches to ON, and controls the switches of the remaining phases by pulse width modulation. (Pulse Width Modulation) mode and a second PWM mode in which the switches of all phases among the six switches are controlled by pulse width modulation.

In FIG. 2, a first period T1 is a period during which the control section 12 operates in the first PWM mode. In the following description, the first period T1 may be referred to as the first PWM mode period. The first PWM mode period T1 is divided into a high side continuous ON period T1H and a low side continuous ON period T1L. During the high-side continuous ON period T1H, the control unit 12 fixes the U-phase high-side switch _QUH of the six switches to ON, and controls the remaining V-phase and W-phase switches by pulse width modulation. During the low-side continuous ON period T1L, the control unit 12 fixes the W-phase low-side switch _QWL of the six switches to ON, and controls the remaining U-phase and V-phase switches by pulse width modulation. The remaining phase switches include the remaining phase high-side switches and low-side switches.

In FIG. 2, the second period T2 is the period during which the control section 12 operates in the second PWM mode. In the following description, the second period T2 may be referred to as a second PWM mode period. During the second PWM mode period T2, the control unit 12 controls the switches of all phases among the six switches by pulse width modulation. All-phase switches include all-phase high-side switches and low-side switches. The control unit 12 periodically switches between the first PWM mode and the second PWM mode in the first modulation mode period TM1. As a result, as shown in FIG. 2, the first PWM mode period T1 and the second PWM mode period T2 appear alternately in the first modulation mode period TM1.

Hereinafter, the mode in which the control unit 12 fixes the high-side switch of one phase out of the six switches to ON and controls the switches of the remaining phases by pulse width modulation is referred to as a third PWM mode. A mode in which the control unit 12 fixes one phase low-side switch of the six switches to ON and controls the remaining phase switches by pulse width modulation is called a fourth PWM mode. The high side continuous ON period T1H is a period during which the control section 12 operates in the third PWM mode. The low-side continuous ON period T1L is a period during which the controller 12 operates in the fourth PWM mode.

The control unit 12 alternately switches between the third PWM mode and the fourth PWM mode as the first PWM mode during the first modulation mode period TM1. As a result, as shown in FIG. 2, in the first modulation mode period TM1, the high-side continuous ON period T1H and the low-side continuous ON period T1L interpose the second PWM mode period T2 therebetween. appear alternately.

In the first PWM mode period T1, the ON period of each phase in one cycle of pulse width modulation, that is, the duty of each phase, is uniformly offset from the duty when the second PWM mode is applied to the ON period of each phase. is the value Specifically, in the case of the high side continuous ON period T1H, the phase having the maximum duty among the duties of the respective phases when the second PWM mode is applied to the high side continuous ON period T1H has a duty of 100%. , the duties of all phases are uniformly offset. In the case of the low-side continuous ON period T1L, the duty of all phases is adjusted so that the minimum duty among the phases when the second PWM mode is applied to the low-side continuous ON period T1L is 0%. are uniformly offset. As a result, the phase-to-phase voltage in the first PWM mode period T1 and the phase-to-phase voltage in the second PWM mode period T2 match, and smooth motor control is realized.

The sum TS of the first PWM mode period T1 and the second PWM mode period T2 is shorter than 1/2N of one cycle of the electrical angle of the AC waveform appearing at the connection terminal of the power conversion circuit 11 . As described above, in this embodiment, the value of N is 3, so the sum TS of the first PWM mode period T1 and the second PWM mode period T2 is 1/6 of one period of the electrical angle. is also short. The sum TS of the first PWM mode period T1 and the second PWM mode period T2 is the sum of a pair of the first PWM mode period T1 and the second PWM mode period T2 adjacent on the time axis. . Hereinafter, the sum TS of the first PWM mode period T1 and the second PWM mode period T2 may be referred to as a mode switching period.

The first PWM mode period T1 is longer than one period of pulse width modulation. One cycle of pulse width modulation means one cycle of a PWM waveform (rectangular wave) appearing in each gate signal. If the above condition that "the mode switching period TS is shorter than 1/2N of one period of the electrical angle of the AC waveform appearing at the connection terminal of the power conversion circuit 11" is satisfied, then the second PWM mode period T2 The length is not particularly limited. As an example, in FIG. 2, the first PWM mode period T1 has a length corresponding to one period of pulse width modulation, and the second PWM mode period T2 has a length corresponding to 1.5 periods of pulse width modulation. have In this case, the mode switching period TS corresponds to 2.5 periods of pulse width modulation. For example, when 90 periods of pulse width modulation are included in one period of electrical angle, 1/6 of one period of electrical angle corresponds to 15 periods of pulse width modulation. The period is sufficiently shorter than 1/6 of one period.

The ratio of the first PWM mode period T1 to the sum of the first PWM mode period T1 and the second PWM mode period T2 is variable. In the following description, the ratio of the first PWM mode period T1 to the sum of the first PWM mode period T1 and the second PWM mode period T2 may be referred to as a mode ratio. As the first PWM mode period T1 becomes longer relative to the second PWM mode period T2, the mode ratio becomes larger. On the other hand, when the second PWM mode period T2 becomes relatively longer than the first PWM mode period T1, the mode ratio becomes smaller.

When the control unit 12 operates in the first modulation mode with the mode ratio relatively large, the ratio of the period during which switching of one phase is stopped in the first modulation mode period TM1 increases, so the switching loss is become relatively small. This corresponds to a state close to the characteristics of two-phase modulation. Therefore, the phase current ripple becomes relatively large. On the other hand, when the control unit 12 operates in the first modulation mode with the mode ratio relatively small, the ratio of the period during which switching of one phase is stopped in the first modulation mode period TM1 becomes small. Losses are relatively large. This corresponds to a state close to the characteristics of three-phase modulation. Therefore, the phase current ripple becomes relatively small. Thus, the higher the mode ratio, the closer the characteristics of the first modulation mode to the two-phase modulation. Also, the smaller the mode ratio, the closer the characteristics of the first modulation mode to the three-phase modulation.

As described above, in the first embodiment, the mode switching period TS, which is the sum of the first PWM mode period T1 and the second PWM mode period T2, is the electric current of the AC waveform appearing at the connection terminal of the power conversion circuit 11. Shorter than 1/6 of one angular period. According to the first embodiment, the first PWM mode corresponding to two-phase modulation and the second PWM mode corresponding to three-phase modulation are switched at a high frequency as compared with the technique of Patent Document 1. be replaced. As a result, it is possible to suppress the switching loss from changing at the timing of switching between the first PWM mode and the second PWM mode, so it is possible to suppress the occurrence of torque unevenness in the first modulation mode period TM1.

In addition, according to the first embodiment, noise can be reduced because the average phase current ripple in the first modulation mode period TM1 can be reduced compared to the case where each switch is controlled only by two-phase modulation. Since the motor 20 is a kind of filter that has an inductance component, by speeding up the switching speed between the first PWM mode and the second PWM mode, the switching loss and the phase current ripple caused by the mode switching can be reduced. can reduce the impact.

FIG. 3 is a diagram showing phase current waveforms obtained by performing a simulation assuming that the gate signals shown in FIG. 2 are used to control each switch in the first modulation mode. Note that the simulation was performed under the condition that the rotation angle of the motor 20 was fixed at a predetermined value in order to ignore the current fluctuation accompanying the rotation of the motor 20 and focus only on the phase current ripple. For comparison, Fig. 3 shows phase current waveforms obtained by performing a simulation assuming that each switch is controlled only by 3-phase modulation, and control of each switch by Min-type 2-phase modulation alone. Phase current waveforms obtained by performing an assumed simulation are shown. Min-type two-phase modulation means so-called low-side-on fixed two-phase modulation. The fixed low-side on-type two-phase modulation is a two-phase modulation method in which one low-side switch of six switches is fixed on and the switches of the remaining phases are controlled by pulse width modulation. In the low-side on-fixed two-phase modulation, the phase switching cycle in which the low-side switch is fixed on corresponds to one-third of one cycle of the electrical angle. Each phase current waveform is the waveform of the W-phase current Iw.

FIG. 4 is a diagram showing the magnitude of the phase current ripple shown in FIG. 3 as the standard deviation of the current values. As shown in FIG. 4, according to the first embodiment, the average phase current ripple can be reduced as compared with the case where each switch is controlled only by Min-type two-phase modulation. As in the example of the gate signal shown in FIG. 2, the first PWM mode period T1 has a length corresponding to one cycle of the pulse width modulation, and the second PWM mode period T2 has a length of 1.5 cycles of the pulse width modulation. If it has a length corresponding to the period, the switching frequency in the first modulation mode period TM1 is 13/15 compared to the case where each switch is controlled only by three-phase modulation. Therefore, according to the first embodiment, switching loss can be reduced compared to the case where each switch is controlled only by three-phase modulation.

According to the first embodiment, for example, the state of the first modulation mode is changed from a state close to the characteristics of two-phase modulation (a state in which the mode ratio is relatively large) to a state close to the characteristics of three-phase modulation (a state in which the mode ratio is compared). By gradually changing the mode ratio from a large value to a small value when switching to a state with a small target, the transition from a state close to the characteristics of two-phase modulation to a state close to the characteristics of three-phase modulation progresses gradually. . As a result, it is possible to reduce abrupt changes in noise caused by switching from a state close to the two-phase modulation characteristics to a state close to the three-phase modulation characteristics, thereby preventing the user from feeling discomfort.

Similarly, when switching the state of the first modulation mode from a state close to the characteristics of three-phase modulation to a state close to the characteristics of two-phase modulation, the mode ratio is gradually changed from a small value to a large value. The transition from a state close to the characteristics of phase modulation to a state close to the characteristics of two-phase modulation progresses gradually. As a result, it is possible to reduce a sudden change in noise caused by switching from a state close to characteristics of three-phase modulation to a state close to characteristics of two-phase modulation, so that it is possible to prevent the user from feeling discomfort.

In the first embodiment, the control unit 12 alternately switches between the third PWM mode and the fourth PWM mode as the first PWM mode during the first modulation mode period TM1. As a result, in the first modulation mode period TM1, the high side continuous ON period T1H and the low side continuous ON period T1L alternately appear as the first PWM mode period T1. Thereby, the switching loss in the high side continuous ON period T1H and the switching loss in the low side continuous ON period T1L are averaged over the entire period of the first modulation mode period TM1. As a result, a balance is maintained between the amount of heat generated during the high-side continuous ON period T1H and the amount of heat generated during the low-side continuous ON period T1, so overheating of the power conversion circuit 11 during the first modulation mode period TM1 can be suppressed.

In the first embodiment, the high side continuous ON period T1H during which the control section 12 operates in the third PWM mode and the low side continuous ON period T1L during which the control section 12 operates in the fourth PWM mode match. In the example shown in FIG. 2, each of the high side continuous ON period T1H and the low side continuous ON period T1L has a length corresponding to one period of pulse width modulation.

This improves the balance between the amount of heat generated during the high-side continuous ON period T1H and the amount of heat generated during the low-side continuous ON period T1L, thereby more effectively suppressing overheating of the power conversion circuit 11 during the first modulation mode period TM1. can.

In the above-described first embodiment, the control unit 12 alternately switches between the third PWM mode and the fourth PWM mode as the first PWM mode during the first modulation mode period TM1. However, the invention is not so limited.

For example, the control unit 12 may control each switch using only the third PWM mode as the first PWM mode during the first modulation mode period TM1. In this case, all first PWM mode periods T1 included in the first modulation mode period TM1 are high side continuous ON periods T1H. Further, for example, the control unit 12 may control each switch using only the fourth PWM mode as the first PWM mode during the first modulation mode period TM1. In this case, all first PWM mode periods T1 included in the first modulation mode period TM1 are low side continuous ON periods T1L.

Furthermore, in the first PWM mode period T1, the control unit 12 sets the third PWM mode and the fourth PWM mode to 2N of one cycle of the electrical angle of the AC waveform appearing at the connection terminal of the power conversion circuit 11. It may be switched at a period shorter than one. For example, when the value of N is 3, the control unit 12 sets the third PWM mode and the fourth PWM mode to 1/6 of one period of the electrical angle in the first PWM mode period T1. You may switch in a period shorter than. In this case, the high side continuous ON period T1H and the low side continuous ON period T1L alternately appear in each of the first PWM mode periods T1 included in the first modulation mode period TM1. Thus, in the first PWM mode period T1, the switching loss in the high side continuous ON period T1H and the switching loss in the low side continuous ON period T1L are averaged. As a result, a balance is maintained between the amount of heat generated during the high-side continuous ON period T1H and the amount of heat generated during the low-side continuous ON period T1, so overheating of the power conversion circuit 11 during the first PWM mode period T1 can be suppressed.

As described above, when the control unit 12 switches between the third PWM mode and the fourth PWM mode during the first PWM mode period T1, the control unit 12 switches between the third PWM mode and the fourth PWM mode during the first PWM mode period T1. The high-side continuous ON period T1H during which the control unit 12 operates in the PWM mode 3 may coincide with the low-side continuous ON period T1L during which the control unit 12 operates in the fourth PWM mode.

This improves the balance between the amount of heat generated during the high-side continuous ON period T1H and the amount of heat generated during the low-side continuous ON period T1L, thereby more effectively suppressing overheating of the power conversion circuit 11 during the first PWM mode period T1. can. [Second embodiment]
Next, a second embodiment of the invention will be described. The second embodiment differs from the first embodiment in that the control section 12 has not only the first modulation mode but also the second modulation mode and the third modulation mode as modulation modes. Therefore, the operation of the control unit 12 in the second embodiment will be described in detail below.

In the second embodiment, the control unit 12 selects a second modulation mode in which the mode ratio is the first ratio and a third modulation mode in which the mode ratio is a second ratio smaller than the first ratio. When switching the modulation mode between, operate in the first modulation mode in the period between the period of operation in the second modulation mode and the period of operation in the third modulation mode, and the first modulation mode The mode ratio is changed continuously or stepwise during the period of operation.

FIG. 5 shows a U-phase high-side gate signal G1 and a V-phase gate signal G1 output during periods when the controller 12 in the second embodiment operates in the first modulation mode, the second modulation mode, and the third modulation mode, respectively. FIG. 10 is a diagram showing an example of a high-side gate signal G3 and a W-phase high-side gate signal G5; In FIG. 5, a period TM2 is a period during which the control section 12 operates in the second modulation mode, and a period TM3 is a period during which the control section 12 operates in the third modulation mode. In the following description, the period TM2 during which the control unit 12 operates in the second modulation mode is referred to as the second modulation mode period, and the period TM3 during which the control unit 12 operates in the third modulation mode is referred to as the third modulation mode. Sometimes called a period.

The second modulation mode differs from the first modulation mode in that the mode ratio is fixed at a first ratio that is greater than the mode ratio of the first modulation mode, and is otherwise similar to the first modulation mode. matches. That is, in the second modulation mode, the control unit 12 periodically switches between the first PWM mode and the second PWM mode while the mode ratio is fixed at the first ratio.

In the example shown in FIG. 5, the control unit 12 alternately switches between the third PWM mode and the fourth PWM mode as the first PWM mode during the second modulation mode period TM2. As a result, as shown in FIG. 5, in the second modulation mode period TM2, as the first PWM mode period T1, the high side continuous ON period T1H and the low side continuous ON period T1L are interposed between them. They appear alternately with the PWM mode period T2 interposed therebetween.

As an example, in FIG. 5, in the second modulation mode period TM2, the first PWM mode period T1 has a length corresponding to three periods of pulse width modulation, and the second PWM mode period T2 has a length corresponding to three cycles of pulse width modulation. has a length corresponding to 1.5 periods of . That is, in the example shown in FIG. 5, the mode ratio of the second modulation mode is fixed at 3/4.5. Below, the mode ratio of the second modulation mode may be referred to as a second mode ratio Rm2.

The third modulation mode is similar to the first modulation mode and the second modulation mode in that the mode ratio is fixed at a second ratio that is less than the mode ratios of the first modulation mode and the second modulation mode. It is different and otherwise consistent with the first modulation mode and the second modulation mode. That is, in the third modulation mode, the control unit 12 periodically switches between the first PWM mode and the second PWM mode while the mode ratio is fixed at the second ratio.

In the example shown in FIG. 5, the control unit 12 alternately switches between the third PWM mode and the fourth PWM mode as the first PWM mode during the third modulation mode period TM3. As a result, as shown in FIG. 5, in the third modulation mode period TM3, as the first PWM mode period T1, the high side continuous ON period T1H and the low side continuous ON period T1L are interposed between them. They appear alternately with the PWM mode period T2 interposed therebetween.

As an example, in FIG. 5, in the third modulation mode period TM3, the first PWM mode period T1 has a length corresponding to one period of pulse width modulation, and the second PWM mode period T2 has a length corresponding to one period of pulse width modulation. has a length corresponding to 3.5 periods of . That is, in the example shown in FIG. 5, the mode ratio of the third modulation mode is fixed at 1/4.5. Hereinafter, the mode ratio of the third modulation mode may be referred to as third mode ratio Rm3.

In the example shown in FIG. 5, similarly to the first embodiment, the control unit 12 alternates between the third PWM mode and the fourth PWM mode as the first PWM mode in the first modulation mode period TM1. switch to As a result, as shown in FIG. 5, in the first modulation mode period TM1, as the first PWM mode period T1, the high side continuous ON period T1H and the low side continuous ON period T1L are interposed between them. They appear alternately with the PWM mode period T2 interposed therebetween.

As an example, in FIG. 5, in the first modulation mode period TM1, the first PWM mode period T1 has a length corresponding to one period of pulse width modulation, and the second PWM mode period T2 has a length corresponding to one period of pulse width modulation. has a length corresponding to 1.5 periods of . That is, in the example shown in FIG. 5, the mode ratio of the first modulation mode is 1/2.5, but in the second embodiment, the control unit 12 sets the mode ratio to is changed continuously or stepwise. Hereinafter, the mode ratio of the first modulation mode may be referred to as a first mode ratio Rm1.

Let Rm1_max be the maximum value of the first mode ratio Rm1, and Rm1_min be the minimum value of the first mode ratio Rm1. The first mode ratio Rm1 is changed continuously or stepwise within the range.

Rm1_min ≤ Rm1 ≤ Rm1_max (1)
The relationship between the first mode ratio Rm1 and the second mode ratio Rm2 is represented by the following formula (2). The relationship between the first mode ratio Rm1 and the third mode ratio Rm3 is represented by the following formula (3). The relationship between the second mode ratio Rm2 and the third mode ratio Rm3 is represented by the following formula (4).

Rm2>Rm1_max (2)
Rm1_min > Rm3 (3)
Rm2 > Rm3 (4)
As described above, the second mode ratio Rm2 is the largest among the first mode ratio Rm1, the second mode ratio Rm2, and the third mode ratio Rm3. Moreover, the third mode ratio Rm3 is the smallest among the first mode ratio Rm1, the second mode ratio Rm2, and the third mode ratio Rm3. Therefore, in the second modulation mode period TM2 in which the control unit 12 operates in the second modulation mode, the control unit 12 controls each switch in a state close to the two-phase modulation characteristics, so switching loss is relatively small. However, the phase current ripple becomes relatively large. On the other hand, during the third modulation mode period TM3 in which the control unit 12 operates in the third modulation mode, the control unit 12 controls each switch in a state close to the characteristics of three-phase modulation, so the phase current ripple is relatively It will be small, but the switching loss will be relatively large.

If the second modulation mode and the third modulation mode were to be instantaneously switched, torque fluctuation would occur due to a sudden change in switching loss, and a sudden change in noise would make the user uncomfortable. There is a risk of giving However, in the second embodiment, the control unit 12 switches between the second modulation mode period TM2 and the third modulation mode when switching the modulation mode between the second modulation mode and the third modulation mode. The first modulation mode is operated in the period between the period TM3, and the first mode ratio Rm1 in the first modulation mode period TM1 is continuously or stepwise within the range represented by the above formula (1) change to

For example, when switching the modulation mode from the third modulation mode to the second modulation mode, the control unit 12 first sets the third mode ratio Rm3 to 1/4.5 in the third modulation mode. After operating, it transitions to the first modulation mode. After shifting to the first modulation mode, the control unit 12 changes the first mode ratio Rm1 from 1/3.5 (Rm1_min)→1/2.5→2/3 . 5 (Rm1_max), and after operating in the first modulation mode, it shifts to the second modulation mode. After shifting to the second modulation mode, the control unit 12 operates in the second modulation mode with the second mode ratio Rm2 fixed at 3/4.5.

For example, when the control unit 12 switches the modulation mode from the second modulation mode to the third modulation mode, first, in the second modulation mode with the second mode ratio Rm2 fixed at 3/4.5, After operating, it transitions to the first modulation mode. After shifting to the first modulation mode, the control unit 12 changes the first mode ratio Rm1 from 2/3.5 (Rm1_max)→1/2.5→1/3 . 5 (Rm1_min) and after operating in the first modulation mode, it shifts to the third modulation mode. After shifting to the third modulation mode, the control section 12 operates in the third modulation mode with the third mode ratio Rm3 fixed at 1/4.5.

As described above, according to the second embodiment, when the control unit 12 switches the modulation mode between the second modulation mode and the third modulation mode, the second modulation mode period TM2 and By continuously or stepwise changing the first mode ratio Rm1 in the first modulation mode period TM1 between the third modulation mode period TM3, the second modulation mode close to the characteristics of the two-phase modulation and the Modulation mode transition gradually progresses to the third modulation mode, which is close to the characteristics of three-phase modulation. As a result, a sudden change in switching loss and a sudden change in noise due to switching of the modulation mode can be suppressed, so that fluctuations in the torque of the motor 20 can be suppressed and uncomfortable feeling given to the user can be suppressed.

The control unit 12 alternately switches between the third PWM mode and the fourth PWM mode as the first PWM mode during the second modulation mode period TM2. As a result, in the second modulation mode period TM2, the high side continuous ON period T1H and the low side continuous ON period T1L alternately appear as the first PWM mode period T1.

As a result, the switching loss in the high side continuous ON period T1H and the switching loss in the low side continuous ON period T1L are averaged over the entire second modulation mode period TM2. As a result, a balance is maintained between the amount of heat generated during the high-side continuous ON period T1H and the amount of heat generated during the low-side continuous ON period T1, so overheating of the power conversion circuit 11 during the second modulation mode period TM2 can be suppressed. The same is true for the third modulation mode period TM3.

In the second modulation mode period TM2, the high side continuous ON period T1H during which the control unit 12 operates in the third PWM mode and the low side continuous ON period T1L during which the control unit 12 operates in the fourth PWM mode coincide. do. In the example shown in FIG. 5, in the second modulation mode period TM2, the high side continuous ON period T1H and the low side continuous ON period T1L each have a length corresponding to three cycles of pulse width modulation.

This improves the balance between the amount of heat generated during the high-side continuous ON period T1H and the amount of heat generated during the low-side continuous ON period T1L, thereby more effectively suppressing overheating of the power conversion circuit 11 during the second modulation mode period TM2. can. The same is true for the third modulation mode period TM3.

In the second embodiment, the control unit 12 switches the third PWM mode and the fourth PWM mode to the first PWM mode in the second modulation mode period TM2 and the third modulation mode period TM3. , the present invention is not limited to this. For example, the control unit 12 may control each switch using only the third PWM mode as the first PWM mode in at least one of the second modulation mode period TM2 and the third modulation mode period TM3. good. Also, for example, the control unit 12 controls each switch using only the fourth PWM mode as the first PWM mode in at least one of the second modulation mode period TM2 and the third modulation mode period TM3. may

Furthermore, in the second modulation mode period TM2, the control unit 12 sets the third PWM mode and the fourth PWM mode to 2N of one cycle of the electrical angle of the AC waveform appearing at the connection terminal of the power conversion circuit 11. It may be switched at a period shorter than one. For example, when the value of N is 3, the control unit 12 sets the third PWM mode and the fourth PWM mode to 1/6 of one cycle of the electrical angle in the second modulation mode period TM2. You may switch in a period shorter than.

Thus, in the second modulation mode period TM2, the switching loss during the high side continuous ON period T1H and the switching loss during the low side continuous ON period T1L are averaged. As a result, a balance is maintained between the amount of heat generated during the high-side continuous ON period T1H and the amount of heat generated during the low-side continuous ON period T1, so overheating of the power conversion circuit 11 during the second modulation mode period TM2 can be suppressed.

As described above, when the control unit 12 switches between the third PWM mode and the fourth PWM mode in the second modulation mode period TM2, the control unit 12 operates in the third PWM mode. The continuous ON period T1H may coincide with the low side continuous ON period T1L during which the controller 12 operates in the fourth PWM mode.

This improves the balance between the amount of heat generated during the high-side continuous ON period T1H and the amount of heat generated during the low-side continuous ON period T1L, thereby more effectively suppressing overheating of the power conversion circuit 11 during the second modulation mode period TM2. can. [Third Embodiment]
Next, a third embodiment of the invention will be described. In the third embodiment, the second mode ratio Rm2 (first ratio in the second modulation mode) is 1 and the third mode ratio Rm3 (second ratio in the third modulation mode) is 0. It is different from the second embodiment in that there is

FIG. 6 shows a U-phase high-side gate signal G1 and a V-phase gate signal G1 output during periods when the controller 12 in the third embodiment operates in the first modulation mode, the second modulation mode, and the third modulation mode, respectively. FIG. 10 is a diagram showing an example of a high-side gate signal G3 and a W-phase high-side gate signal G5;

As shown in FIG. 6, when the second mode ratio Rm2 is 1, the control unit 12 operates only in the first PWM mode corresponding to two-phase modulation over the entire period of the second modulation mode period TM2. do. That is, the second modulation mode period TM2 is equal to the first PWM mode period T1. In the example shown in FIG. 6, the controller 12 operates in the fourth PWM mode as the first PWM mode during the second modulation mode period TM2. That is, the second modulation mode period TM2 is equal to the low side continuous ON period T1L.

As shown in FIG. 6, when the third mode ratio Rm3 is 0, the control unit 12 operates only in the second PWM mode corresponding to three-phase modulation over the entire period of the third modulation mode period TM3. do. That is, the third modulation mode period TM3 is equal to the second PWM mode period T2.

In the example shown in FIG. 6, the control unit 12 uses only the fourth PWM mode as the first PWM mode during the first modulation mode period TM1. As a result, as shown in FIG. 6, only the low side continuous ON period T1L appears as the first PWM mode period T1 in the first modulation mode period TM1. As in the second embodiment, the control unit 12 continuously or stepwise changes the first mode ratio Rm1 within the range represented by the above formula (1) in the first modulation mode period TM1.

As described above, according to the third embodiment, the control unit 12 operates only in the first PWM mode corresponding to two-phase modulation over the entire period of the second modulation mode period TM2. The switching loss in the second modulation mode period TM2 can be reduced compared to the mode. Further, according to the third embodiment, the control unit 12 operates only in the second PWM mode corresponding to three-phase modulation over the entire period of the third modulation mode period TM3. As a result, the phase current ripple in the third modulation mode period TM3 can be reduced.

Furthermore, according to the third embodiment, as in the second embodiment, the control unit 12 controls the Modulation mode transition between a second modulation mode corresponding to two-phase modulation and a third modulation mode corresponding to three-phase modulation by continuously or stepwise changing the first mode ratio Rm1 progresses gradually. As a result, a sudden change in switching loss and a sudden change in noise due to switching of the modulation mode can be suppressed, so that fluctuations in the torque of the motor 20 can be suppressed and uncomfortable feeling given to the user can be suppressed.

6 shows the case where the control unit 12 operates in the fourth PWM mode as the first PWM mode in the second modulation mode period TM2, but the control unit 12 operates in the second modulation mode It may operate in the third PWM mode during the mode period TM2. [Fourth embodiment]
Next, a fourth embodiment of the invention will be described. The fourth embodiment is consistent with the third embodiment in that the second mode ratio Rm2 is 1 and the third mode ratio Rm3 is 0, but the controller 12 controls the second modulation mode period In TM2, the third PWM mode and the fourth PWM mode are alternately switched in a cycle corresponding to one-sixth of one electrical angle cycle of the AC waveform appearing at the connection terminal of the power conversion circuit 11. 3 differs from the embodiment.

FIG. 7 shows a U-phase high-side gate signal G1 and a V-phase gate signal G1 output during periods when the controller 12 in the fourth embodiment operates in the first modulation mode, the second modulation mode, and the third modulation mode, respectively. FIG. 10 is a diagram showing an example of a high-side gate signal G3 and a W-phase high-side gate signal G5;

As shown in FIG. 7, when the second mode ratio Rm2 is 1, the control unit 12 operates only in the first PWM mode corresponding to two-phase modulation over the entire period of the second modulation mode period TM2. do. That is, the second modulation mode period TM2 is equal to the first PWM mode period T1. In the example shown in FIG. 7, the control unit 12 sets the third PWM mode and the fourth PWM mode in the second modulation mode period TM2 with a period corresponding to one-sixth of one period of the electrical angle. alternately with . That is, in the second modulation mode period TM2, the high-side continuous ON period T1H and the low-side continuous ON period T1L alternately appear with a period corresponding to 1/6 of one period of the electrical angle.

As shown in FIG. 7, when the third mode ratio Rm3 is 0, the control unit 12 operates only in the second PWM mode corresponding to three-phase modulation over the entire period of the third modulation mode period TM3. do. That is, the third modulation mode period TM3 is equal to the second PWM mode period T2.

In the example shown in FIG. 7, the control unit 12 alternately switches between the third PWM mode and the fourth PWM mode as the first PWM mode during the first modulation mode period TM1. As a result, as shown in FIG. 7, in the first modulation mode period TM1, as the first PWM mode period T1, the high side continuous ON period T1H and the low side continuous ON period T1L are interposed between them. They appear alternately with the PWM mode period T2 interposed therebetween. As in the third embodiment, the control unit 12 continuously or stepwise changes the first mode ratio Rm1 within the range represented by the above formula (1) in the first modulation mode period TM1.

When the control unit 12 shifts from the first modulation mode to the second modulation mode, in the angle section in which the third PWM mode is applied as the second modulation mode, the low side continuous ON period T1L and the second The ratio with the PWM mode period T2 is decreased, and the ratio of the high side continuous ON period T1H is increased. Further, when the control unit 12 shifts from the first modulation mode to the second modulation mode, in the angle section in which the fourth PWM mode is applied as the second modulation mode, the high side continuous ON period T1H The ratio of the second PWM mode period T2 is decreased to increase the ratio of the low side continuous ON period T1L.

As described above, according to the fourth embodiment, in the second modulation mode period TM2, the control unit 12 switches the third PWM mode and the fourth PWM mode to 6 minutes of one cycle of the electrical angle. By alternately switching with a period corresponding to 1 of , in the second modulation mode period TM2, the high-side continuous ON period T1H and the low-side continuous ON period T1L correspond to 1/6 of the electrical angle 1 period. It appears alternately in cycles.

As a result, the balance between the amount of heat generated in the continuous high-side ON period T1H and the amount of heat generated in the continuous low-side ON period T1 is improved over the entire period of the second modulation mode period TM2. Overheating of the power conversion circuit 11 can be effectively suppressed.

Furthermore, according to the fourth embodiment, as in the third embodiment, the control unit 12 controls the Modulation mode transition between a second modulation mode corresponding to two-phase modulation and a third modulation mode corresponding to three-phase modulation by continuously or stepwise changing the first mode ratio Rm1 progresses gradually. As a result, a sudden change in switching loss and a sudden change in noise due to switching of the modulation mode can be suppressed, so that fluctuations in the torque of the motor 20 can be suppressed and uncomfortable feeling given to the user can be suppressed. [Fifth Embodiment]
Next, a fifth embodiment of the present invention will be described. The fifth embodiment is consistent with the fourth embodiment in that the second mode ratio Rm2 is 1 and the third mode ratio Rm3 is 0, but the controller 12 controls the second modulation mode period In TM2, the third PWM mode and the fourth PWM mode are alternately switched in a period shorter than 1/6 of one electrical angle period of the AC waveform appearing at the connection terminal of the power conversion circuit 11. 4 differs from the embodiment.

FIG. 8 shows a U-phase high-side gate signal G1 and a V-phase gate signal G1 output during periods when the control unit 12 in the fifth embodiment operates in the first modulation mode, the second modulation mode, and the third modulation mode, respectively. FIG. 10 is a diagram showing an example of a high-side gate signal G3 and a W-phase high-side gate signal G5;

As shown in FIG. 8, when the second mode ratio Rm2 is 1, the control unit 12 operates only in the first PWM mode close to the two-phase modulation characteristics over the entire period of the second modulation mode period TM2. Operate. That is, the second modulation mode period TM2 is equal to the first PWM mode period T1. In the example shown in FIG. 8, the control unit 12 sets the third PWM mode and the fourth PWM mode in the second modulation mode period TM2 in a period shorter than one-sixth of one period of the electrical angle. , for example, alternately with a period corresponding to 2.5 periods of the pulse width modulation. That is, in the second modulation mode period TM2, the high side continuous ON period T1H and the low side continuous ON period T1L alternately appear with a period corresponding to 2.5 periods of the pulse width modulation.

As shown in FIG. 8, when the third mode ratio Rm3 is 0, the control unit 12 operates only in the second PWM mode corresponding to three-phase modulation over the entire period of the third modulation mode period TM3. do. That is, the third modulation mode period TM3 is equal to the second PWM mode period T2.

In the example shown in FIG. 8, the control unit 12 alternately switches between the third PWM mode and the fourth PWM mode as the first PWM mode during the first modulation mode period TM1. As a result, as shown in FIG. 8, in the first modulation mode period TM1, as the first PWM mode period T1, a high-side continuous ON period T1H and a low-side continuous ON period T1L are interposed between them. They appear alternately with the PWM mode period T2 interposed therebetween. As in the third embodiment, the control unit 12 continuously or stepwise changes the first mode ratio Rm1 within the range represented by the above formula (1) in the first modulation mode period TM1.

For example, as described above, in the second modulation mode period TM2, the control unit 12 alternately switches between the third PWM mode and the fourth PWM mode at a cycle corresponding to 2.5 cycles of pulse width modulation. In the case of switching, the number of switching times in the second modulation mode period TM2 is 11/15 times the number of switching times in the third modulation mode period TM3. Therefore, according to the fifth embodiment, it is possible to reduce the switching loss during the second modulation mode period TM2 as compared with the third modulation mode period TM3.

Further, according to the fifth embodiment, similarly to the fourth embodiment, the control unit 12 controls the By changing the first mode ratio Rm1 continuously or stepwise, the modulation mode is changed between a second modulation mode close to characteristics of two-phase modulation and a third modulation mode corresponding to three-phase modulation. Migration is gradual. As a result, a sudden change in switching loss and a sudden change in noise due to switching of the modulation mode can be suppressed, so that fluctuations in the torque of the motor 20 can be suppressed and uncomfortable feeling given to the user can be suppressed. [Modification]
The present invention is not limited to the above-described embodiments, and each configuration described in this specification can be appropriately combined within a mutually consistent range.

For example, when applying the third embodiment, the first mode ratio Rm1 in the first modulation mode period TM1 may be changed according to the specific example shown in FIG. FIG. 9 shows a specific example in which the mode switching cycle TS is fixed at four cycles of pulse width modulation, and a specific example in which the mode switching cycle TS is not fixed to a constant value but is variable. showing.

For example, when applying the fifth embodiment, the first mode ratio Rm1 in the first modulation mode period TM1 may be changed according to the specific example shown in FIG. FIG. 10 shows a specific example in which the mode switching cycle TS is fixed at 4.5 cycles of pulse width modulation, and a specific example in which the mode switching cycle TS is not fixed at a constant value but is variable. and

For example, in the above embodiment, the power conversion device 10 that controls the motor 20, which is a three-phase motor, is illustrated, but the motor 20 to be controlled is not limited to a three-phase motor, and is an N-phase motor (n is an integer of 3 or more). ). In the above embodiment, IGBTs are used as the arm switches included in the power conversion circuit 11. However, the arm switches may be switching elements for high power such as MOS-FETs other than IGBTs.

Claims (9)

a power conversion circuit that performs mutual conversion between DC power and N-phase AC power (N is an integer of 3 or more);
a control unit that controls 2N switches included in the power conversion circuit in a first modulation mode;
with
The control unit, in the first modulation mode, fixes a high-side switch or a low-side switch of one phase among the 2N switches to ON, and controls the switches of the remaining phases by pulse width modulation. periodically switching between the PWM mode and a second PWM mode in which all phase switches among the 2N switches are controlled by the pulse width modulation;
The sum of the first period during which the control section operates in the first PWM mode and the second period during which the control section operates in the second PWM mode appears at the connection terminal of the power conversion circuit. Shorter than 1/2N of one cycle of the electrical angle of the AC waveform,
The first period has a length of one cycle or more of the pulse width modulation,
The power conversion device, wherein a ratio of the first period to the sum of the first period and the second period is variable. The control unit selects a modulation mode between a second modulation mode in which the ratio is a first ratio and a third modulation mode in which the ratio is a second ratio smaller than the first ratio. When switching, operating in the first modulation mode during a period between operating in the second modulation mode and operating in the third modulation mode, and operating in the first modulation mode changing the ratio continuously or stepwise during the period of operation;
The power converter according to claim 1. wherein the first ratio in the second modulation mode is 1;
The power converter according to claim 2. wherein the second ratio in the third modulation mode is 0;
The power converter according to claim 2 or 3. a third PWM mode in which the control unit fixes one-phase high-side switch of the 2N switches to ON during the first period and controls the remaining phase switches by the pulse width modulation; , and a fourth PWM mode in which the low-side switch of one phase among the 2N switches is fixed to be ON and the switches of the remaining phases are controlled by the pulse width modulation, and 1/2N of one period of the electrical angle. switch at a shorter period than
The power converter according to any one of claims 2 to 4. In the first period included in the period in which the control unit operates in the first modulation mode, a period in which the control unit operates in the third PWM mode and a period in which the control unit operates in the fourth PWM mode is consistent with the period that works with,
The power converter according to claim 5. In the first period included in the period in which the control unit operates in the second modulation mode, a period in which the control unit operates in the third PWM mode and a period in which the control unit operates in the fourth PWM mode is consistent with the period that works with,
The power converter according to claim 5 or 6. a third PWM mode in which the control unit fixes one-phase high-side switch of the 2N switches to ON during the first period and controls the remaining phase switches by the pulse width modulation; , and a fourth PWM mode in which the low-side switch of one phase among the 2N switches is fixed to be ON and the switches of the remaining phases are controlled by the pulse width modulation, and 1/2N of one period of the electrical angle. switch at a shorter period than
The power converter according to claim 1. In the first period, the period during which the control unit operates in the third PWM mode and the period during which the control unit operates in the fourth PWM mode match.
The power converter according to claim 8.

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